Performance Counter Definitions

Observing Processor Queue Length

The System\Processor Queue Length counter is a rough indicator of the number of threads each processor is servicing. The processor queue length, sometimes called processor queue depth, reported by this counter is an instantaneous value that is representative only of a current snapshot of the processor, so it is necessary to observe this counter over a long period of time. Also, the System\Processor Queue Length counter is reporting a total queue length for all processors, not a length per processor.

The optimal processor queue length can vary based on processor utilization or other factors as follows:

• For busy systems that experience processor utilization in the 80 to 90 percent range and use thread scheduling, the queue length should range from one to three threads per processor. For example, on a four-processor (4P) system, the expected range of processor queue length on a system with high CPU activity is 4 to 12.

• On systems with lower CPU utilization, the processor queue length is typically 0 or 1.

• For systems running services that use fiber scheduling, such as Microsoft® SQL Server™ version 7.0, the typical processor queue length will range between 0 and 1, because there is a single thread on each processor that schedules fibers within the thread. (Fiber scheduling is enabled when the lightweight pooling option is selected.)

If the processor queue length exceeds the value recommended in the preceding list, it generally indicates that there are more threads than the current processor can service in an optimal way. Reducing the number of threads or providing more CPU power, either by adding processors or upgrading to faster processors, are optional methods of shortening the processor queue.

Working Set

The set of memory pages (areas of memory allocated to a process) recently used by the threads in a process. If available memory on the server is above a specified threshold, pages remain in the Working Set of a process even if they are not in use. When available memory falls below a specified threshold, pages are removed from the Working Set. If these pages are needed, they will be returned back to the Working Set before they leave main memory and are made available for other processes to use.

System\Context Switches/sec

The combined average rate at which all processors in the computer are switched from one thread to another. Context switches occur when a running thread voluntarily relinquishes the processor, is preempted by a higher priority ready thread, or switches between user-mode and privileged (kernel) mode to use an Executive or subsystem service. This counter is the sum of Thread\Context Switches/sec for all threads running on all processors in the computer, and it is measured in numbers of switches. There are context switch counters on theSystemandThreadobjects. This counter displays the difference between the values observed in the last two samples, divided by the duration of the sample interval.

Available Mbytes

Displays the amount of physical memory, in bytes, available to processes running on the computer.

Bytes Total/sec

The total rate of bytes transferred by the Web service. This counter is the sum of Bytes Sent/sec and Bytes Received/sec.

Private Bytes

Displays the current number of bytes this process has allocated that cannot be shared with other processes.

Processor\% Processor Time

The average percentage of elapsed time that the processor spends to execute a non-idle thread. It is calculated by measuring the duration of time the idle thread is active in the sample interval, and subtracting that time from the interval duration. (Each processor has an idle thread that consumes cycles when no other threads are ready to run.) This counter is the primary indicator of processor activity, and it displays the average percentage of busy time observed during the sample interval.